In a first aspect, this invention pertains to a process of oxidative halogenation, particularly oxidative chlorination. For the purposes of this discussion, the term xe2x80x9coxidative halogenationxe2x80x9d is defined as a process wherein a hydrocarbon or halogenated hydrocarbon (the xe2x80x9cstarting hydrocarbonxe2x80x9d) is contacted with a source of halogen and a source of oxygen so as to form a halocarbon having a greater number of halogen substituents than the starting hydrocarbon. The term xe2x80x9chalocarbonxe2x80x9d will include halogenated hydrocarbons as well as compounds consisting only of carbon and halogen atoms. In a second aspect, this invention pertains to a novel catalyst for the oxidative halogenation process. In a third aspect, this invention pertains to novel catalyst supports.
Halogenated hydrocarbons, such as 1,2-dichloroethane, 1,2-dibromoethane, dichloropropanes, and dichloropropenes, find utility in numerous applications, such as in fumigants and in the production of monomers useful in polymerization processes. 1,2-Dichloroethane, for example, which is manufactured industrially on a scale of several million tons per year, is converted by thermal dehydrochlorination into vinyl chloride monomer(VCM) and hydrogen chloride. VCM is polymerized into poly(vinyl)chloride (or PVC), a widely used polymer. The hydrogen chloride produced by dehydrochlorination is separated from the VCM and thereafter contacted with ethylene and oxygen in the presence of a catalyst to produce 1,2-dichloroethane. In the prior art, the contacting specifically of ethylene, hydrogen chloride, and oxygen to form 1,2-dichloroethane and water is known as the xe2x80x9coxychlorination reaction.xe2x80x9d
The oxychlorination of ethylene is abundantly described in the patent literature, representative art of which includes U.S. Pat. Nos. 3,634,330, 3,658,367, 3,658,934, 5,972,827, GB 1,039,369, and GB 1,373,296. The catalyst employed in the oxychlorination of ethylene typically contains copper chloride or iron chloride, and optionally, one or more alkali or alkaline earth metal chlorides, and/or optionally, one or more rare earth chlorides, supported on an inert carrier, typically alumina, silica, or an aluminosilicate. Alternatively, the catalyst components can be unsupported, but fused into a molten salt.
Oxidative halogenation processes are quite general and can be extended to a variety of hydrocarbons in addition to ethylene. For example, oxidative chlorination processes are known for the conversion of methane to chloromethanes, ethane to chloroethanes and chloroethenes, and, by analogy, higher saturated hydrocarbons to higher chlorohydrocarbons. This chemistry is not unique to chlorine and can also be extended broadly to other halogens. Halogen sources can comprise hydrogen halides and halohydrocarbons having labile halogens.
One disadvantage of prior art oxidative halogenation processes involves their production of undesirable oxygenated by-products, such as partially oxidized hydrocarbons and deep oxidation products (COx), namely, carbon monoxide and carbon dioxide. Another disadvantage of prior art oxidative halogenation processes involves their production of undesirable oxygenated halocarbon by-products, for example, trichloroacetaldehyde (also known as chloral, CCl3CHO) in the production of 1,2-dichloroethane. The production of unwanted by-products irretrievably wastes the hydrocarbon feed and creates product separation and by-product disposal problems. Any reduction in the quantity of oxygenated products, particularly, oxygenated halocarbons and COx oxygenates would be highly desirable.
In a different aspect, rare earth compounds are known to be promoters in a diverse assortment of catalyzed organic processes, including, for example, oxidations, steam reforming, auto emission reduction, esterification, Fischer-Tropsch synthesis, and the aforementioned oxidative halogenation processes. In the general preparation of rare earth-promoted catalysts, a solution containing a soluble rare earth salt, such as the chloride, is dispersed, for example, by impregnation or ion-exchange, optionally, along with one or more additional catalytic components onto a support or carrier, such as alumina or silica. U.S. Pat. No. 2,204,733 discloses a catalyst containing a compound of copper and a compound of the rare earth group, being prepared by precipitating the metals as hydroxides onto a suitable support, or by soaking or impregnating a support with a solution of copper and rare earth salts, or by precipitating the metals as hydroxides with sodium or potassium hydroxide. The art, in general, appears to be silent with respect to rare earth compounds functioning as catalyst carriers or supports, perhaps because rare earth compounds typically are not found to be porous. Catalyst supports are generally known to require at least some porosity, that is, some void space, such as channels and pores or cavities, which create surface area whereon catalytic metals and components can be deposited.
In one aspect, this invention is a novel oxidative halogenation process of preparing a halocarbon. The novel process of this invention comprises contacting a hydrocarbon or halogenated hydrocarbon with a source of halogen and a source of oxygen in the presence of a catalyst under process conditions sufficient to prepare a halocarbon containing a greater number of halogen substituents than in the starting hydrocarbon or halogenated hydrocarbon, as the case may be, the catalyst comprising copper on a porous rare earth halide support. The term xe2x80x9chalocarbonxe2x80x9d will be understood as including halogenated hydrocarbons as well as compounds consisting only of carbon and halogen atoms.
The oxidative halogenation process of this invention advantageously converts a hydrocarbon or halogenated hydrocarbon in the presence of a source of halogen and a source of oxygen into a halocarbon having an increased number of halogen substituents as compared with the starting hydrocarbon. Accordingly, the process of this invention can be used, in a preferred embodiment, to oxychlorinate ethylene in the presence of hydrogen chloride and oxygen into 1,2-dichloroethane. Since the hydrogen chloride may be derived from the dehydrochlorination of 1,2-dichloroethane, the process of this invention may be easily integrated into a VCM plant, as described hereinabove. As a more preferred advantage, the process of this invention produces lower levels of undesirable by-products, particularly COx oxygenates, namely, carbon monoxide and carbon dioxide, and lower levels of undesirable oxygenated halocarbons, such as chloral, than prior art oxidative halogenation processes. The reduction in undesirable oxygenated by-products translates into a higher selectivity to the desired halocarbon product, lower waste of hydrocarbon feed, and fewer by-product disposal problems. In addition, the better selectivity to the desired halocarbon product allows the process to be operated at higher temperatures for higher conversion.
In a second aspect, this invention is a novel composition of matter comprising copper dispersed on a porous rare earth halide support.
The novel composition of this invention is useful as a catalyst in the oxidative halogenation of hydrocarbons or halogenated hydrocarbons, as exemplified by the oxychlorination of ethylene in the presence of a source of chlorine and oxygen to form 1,2-dichloroethane. Advantageously, the novel catalyst of this invention produces lower levels of by-products, particularly COx oxygenates and oxygenated halocarbons, such as chloral, in the aforementioned oxidative halogenation process. As a second advantage, the unique catalyst composition of this invention does not require a conventional carrier or support, such as alumina or silica. Rather, the catalyst of this invention employs a porous rare earth halide, which uniquely functions both as the catalyst""s support and as a source of a further catalytically active (rare earth) component.
In a third aspect, this invention is a second composition of matter comprising copper dispersed on a porous rare earth oxyhalide support. This second novel composition is a useful catalyst precursor to the catalyst comprising copper dispersed on the porous rare earth halide support, described hereinabove.
In a fourth aspect, this invention claims use of the aforementioned porous rare earth oxyhalide and porous rare earth halide as supports and carriers for catalytic components. The porous rare earth oxyhalide or rare earth halide can be used as a support for any catalytic metal or metallic ion in the Periodic Table of the Elements, as well as any organic or non-metallic inorganic catalyst component.
The porous rare earth oxyhalide or halide support can be advantageously employed in catalysts which benefit from the promoting effects of rare earth elements and/or in catalysts which require basicity. Unlike most catalyst supports of the prior art, the rare earth halide support of this invention is soluble in water. Accordingly, should process equipment, such as filters, valves, circulating tubes, and small or intricate parts of reactors, become plugged with particles of a catalyst containing the rare earth halide support of this invention, then a simple water wash can advantageously dissolve the plugged particles and restore the equipment to working order. As a further advantage, the novel rare earth halide and oxyhalide supports of this invention provide for the easy recovery of costly catalytic metals. The recovery simply involves contacting the spent catalyst containing the catalytic metals and the novel support with acid under conditions sufficient to etch away the catalytic metals. Thereafter, the metals can be recovered from the acidic medium, for example, by precipitation. Any portion of the rare earth support dissolved into the acidic medium can also be recovered by re-precipitation with base.